1. Field of the Invention
This invention is directed to a method and apparatus for monitoring and analyzing, on an on-line basis, the fatigue accumulated by components and systems subjected to fluid flow, thermal and pressure transients, particularly nuclear power plant components and systems. More particularly, the invention is directed to presenting to plant engineers a representation of the margin between current fatigue accumulation and a value of fatigue accumulation that indicates repair, when replacement or refurbishment of the component or system is necessary. The invention also encompasses techniques for providing accurate determination of stresses at plant locations critical to fatigue, the determination being made through measurements of plant process and response parameters.
2. Description of the Related Art
Components in a nuclear power plant are subjected throughout their 40 year nominal life to stresses induced by changes in process fluid temperature and pressure. It is necessary for the operators and engineers of a nuclear power plant to be constantly aware of the status of critical plant components and systems with respect to fatigue. Presently, this is done by the following means: measurements of plant process and response parameters (temperature, pressure, flow, level, valve status, setpoint status, for example) are measured and the data is recorded by a plant computer. This data is used by plant engineers to make subjective judgments regarding certain types of transients. The types of transients that must be recorded are specified in the plant technical specifications, which are overseen by the U.S. Nuclear Regulatory Commission (NRC). The technical specifications allow a specified number of each type of transient during the 40-year life. The prior art methods do not perform fatigue calculations to determine changes in life expectancy, but make educated guesses concerning when a component should be removed from service based on the conservative transient counts allowed by regulators and subjective determinations, by engineers, as to whether a particular transient should be counted. The transients in a nuclear power plant fall into two general categories; normal transients which occur during plant start-up and plant power output demand changes and abnormal transients which occur when a plant component or system is functioning abnormally. If the allowable number for one or more transients is exceeded, justification must be provided to the NRC as to why the plant is safe for continued operation. This may include revision of the stress analysis which formed the original design basis for the plant.